What is the experimental evidence in support of the diea that electronic energies in an atom are quantized?

Explanation

We know that the electrons are fast moving microparticles which have certain specific energies while revolving around the nucleus of an atom. Since electrons can lose enegry only in fixed amounts or bundles called quanta and can not do so in the ground state of an atom, this means that electronic energies are quantised. For more details consult section 2.21.